1. Field of the Invention
The present invention relates to an optical fiber ferrule assembly capable of improving drawing strength of an optical fiber, and relates to an optical connector and an optical module using the same.
2. Description of the Related Art
Referring now to FIGS. 9-11 a ferrule assembly used in an optical connector, an optical module, an optical measuring instrument, and the like is configured in such a manner that a fixing member 4 is formed integrally with a ferrule body 7 having a tapered hole, with a diameter that is larger towards the rear end to guide the insertion of a bare optical fiber 1, into which the bare optical fiber 1 and a jacketed optical fiber (optical fiber core) 8 are inserted and fixed, respectively. In the conventional ferrule assembly, the fixing member 4 is filled with an adhesive 9 in advance, and the bare optical fiber 1, an end coating of which is removed, is inserted into a central hole 5 thereof until a coating layer of the jacketed optical fiber 8 following the bare optical fiber 1 comes into contact with the ferrule body 7. After the insertion, the adhesive 9 is cured, thereby bonding the bare optical fiber 1 and the jacketed optical fiber 8.
However, in an optical connector and an optical module using the conventional optical fiber ferrule assembly manufactured in such a way, when tensile stress is applied thereto during service, the optical fiber is broken and is come out by a small tensile stress of about 0.5 kgf. The causes of such a break of the fiber could be as follows:    (1) When inserting the optical fiber into the ferrule body, the optical fiber is damaged.    (2) When the tensile stress is applied, some portions are subjected to stress concentration, thereby breaking the optical fiber.
With regard to (1), since the assembly is manufactured in such a way that after the adhesive 9 has been charged, the fiber is then inserted, it is conceivable that the possibility of (1) may be small. On the other hand, as for the cause (2), it is conceivable that a local stress may be applied to a boundary point at which the optical fiber is bonded or a boundary point at which the jacketed optical fiber is bonded due to an eccentricity of the central hole 5 of the ferrule body 7 or an eccentricity of the jacketed optical fiber (fiber core) 8, thereby causing the optical fiber to be bent. In general, while the eccentricity of the central hole 5 is as small as 1.5 an or less, the accuracy of the inside diameter of a central hole (insertion hole) of the fixing member 4 is about tens of ems, and the eccentricity of the jacketed optical fiber 8 is also about tens of ems. Accordingly, it is possible that the eccentricity of the optical fiber with respect to the ferrule body 7 exceeds 100 μm.
Thus, in order to determine whether or not the eccentricity has a bearing on the cause of a decrease in the drawing strength of the optical fiber, the optical fiber ferrule assembly of a product group having a small drawing strength is polished in parallel with the optical axis until the bonded optical fiber 1 is exposed, and a state of enclosing the optical fiber 1 into the ferrule body 7 and the fixing member 4 with a flange is observed in detail by a microscope.
As a result, the optical fiber 1 is bent at a boundary point A1 where the optical fiber 1 is bonded to the ferrule body 7 and a boundary point B1 where the optical fiber 1 is bonded to the jacketed optical fiber 8, as shown in FIG. 11, and the state thereof agrees with the state of the optical fiber in the optical fiber ferrule assembly in which the optical fiber is broken and drawn out. Consequently, it is found that a main cause of a decrease in drawing strength, that is, a main cause of the break is stress concentration at the boundaries, particularly, at point A1.